(1) Field of the Invention
The present invention relates to a printing system for performing high-grade printing in a dot printer in which letters or symbols are printed by aggregated dots.
(2) Description of the Prior Art
The conventional high-grade printing system in the dot printer will now be described with reference to the accompanying drawings.
FIG. 1-(I) shows a basic dot pattern, and FIGS. 1-(II) and 1-(III) show a high-grade printing pattern. FIGS. 2-(I) and 2-(II) show two different printing patterns, and FIG. 2-(III) shows the high-grade printing pattern. In the drawings, numeral 4 is used as an example of the pattern.
In the first conventional system, shown in FIG. 1-(I), the number of wires of a printing head is increased and dots are arranged in zigzags to form a high-density dot arrangement. This system is defective in that though high-grade printing can be attained, the structure and control of the apparatus are complicated and the apparatus is expensive.
In the second system, the basic pattern shown in FIG. 1-(I) is slightly shifted in the horizontal direction as shown in FIG. 1-(II) and printing is carried out again. A system in which the basic pattern is slightly shifted in the vertical direction and printing is carried out again is shown in FIG. 1-(III). According to the printing system of the FIG. 1-(II) and FIG. 1-(III) type, the operation is simple and apparatus is not expensive. However, the system is defective in that the quality of printed letters is poor.
As a third system, two different patterns, such as those shown in FIGS. 2-(I) and 2-(II), are slightly shifted in the vertical direction to obtain high-grade printing as shown in FIG. 2-(III). This system is defective in that since two different letter patterns are necessary, the memory capacity is increased and the apparatus is expensive.